Trump tweeted his decision Thursday after departing Washington for a world leader summit in Argentina, where he and Putin were to meet.

Trump says "based on the fact that the ships and sailors have not been returned to Ukraine from Russia, I have decided it would be best for all parties concerned to cancel my previously scheduled meeting in Argentina with President Vladimir Putin. I look forward to a meaningful Summit again as soon as this situation is resolved!"

Russia recently seized three Ukrainian vessels and crews. Russia said Ukraine didn't have permission to pass between Russia's mainland and the Crimean Peninsula. Ukraine insisted its vessels abided by maritime laws.